The present invention relates to a jib stretching and folding device in a wheel type crane such as a truck crane and a rough terrain crane for stretching and folding a strut type jib (which will be hereinafter referred simply to as a jib) in a so-called jib twisting fashion.
There will first be described a basic construction of the prior art device for stretching and folding the jib in the twisting fashion and a folding operation of the jib with reference to FIGS. 26 to 29.
(I) A boom 1 is provided at its forward end portion with a pair of jib mounting shafts 11 and 12 projecting laterally in opposite directions.
(II) A jib 2 has a pair of left and right beams 2a and 2b (the terms "left" and "right" will be hereinafter defined as viewed from an operator cab under the stretched condition of the jib), and the left and right beams 2a and 2b are provided at their respective base ends with a pair of formed jib feet 21 and 22 adapted to be disengageably connected to the jib mounting shafts 11 and 12, respectively.
(III) The left jib foot 21 is a movable jib foot rotatable about its axis, and the right jib foot 22 is a fixed jib foot non-rotatable about its axis.
(IV) When the jib 2 is used, the movable jib foot 21 is engaged with the left jib mounting shaft 11, and the fixed jib foot 22 is engaged with the right jib mounting shaft 12. Under this condition, the jib 2 is stretched from the forward end of the boom 1, and is supported by a suspension rod S.